In recent years, the uses of a liquid crystal display using a liquid crystal panel have been increased to a large-screen TV with upsizing of the board size and improvement in the manufacturing technologies such as a decreasing technology of the defective density as well as large improvement of the display performance because of improvement of contrast and viewing angle dependency. The large-screen TV use assumes moving image display and the image move distance per unit time increases with upsizing of the screen and thus excellent moving image performance is required. Further, blurring at the moving image display time becomes still more conspicuous because of high resolution based on high-definition TV of broadcast video. Still more excellent moving image performance will be required in the future (high-definition TV will become serious).
However, the liquid crystal panel involves a problem in the moving image performance because of the following major causes:
The first cause is as follows: The response speed indicating the time interval between the rising start of a liquid crystal molecule and the rising completion and the time interval between the falling start and the falling completion is low (a dozen or so ms). The liquid crystal panel produces display using a phenomenon in which the arrangement state of liquid crystal molecules changes in response to the applied voltage. Therefore, the changing speed of the arrangement state of liquid crystal molecules restricts the change speed of the display state.
The second cause is as follows: The display system is hold display of keeping given luminance constant for the duration of one display field for display (active matrix type of hold display is used for liquid crystal TV) and thus a feeling of physical disorder occurs for the visual appreciation of a human being as compared with impulse display like a CRT (Cathode Ray Tube) and an image is blurred. FIG. 12A shows the response waveform of a general liquid crystal panel and FIG. 12B shows the response waveform of a general CRT. FIGS. 12A and 12B show the case where white display is produced for the duration of four display fields in black display.
Measures against the first cause are as follows: Optimization is implemented in such a manner that liquid crystal material is put into low viscosity to allow liquid crystal molecules to easily move or that the liquid crystal cell gap is narrowed for enhancing the electric field strength, and an OCB (optical compensated bent) mode of placing the arrangement of liquid crystal molecules in liquid crystal cell in a bend form to hasten motion of the liquid crystal molecules is adopted, so that the response speed of liquid crystal can be improved to about 5 ms sufficiently shorter than one display field (16.7 ms).
The response speed of liquid crystal generally is defined as follows: In FIG. 12A, assuming that the state of luminance A (white) is 100% and the state of luminance B (black) is 0% in a change curve between the luminance A at the white display time and the luminance B at the black display time, the time required for changing from 10% to 90% at the rising time is rising time τr and the time required for changing from 90% to 10% at the falling time is falling time τd.
On the other hand, various propositions are made to improve the problem of the hold display of the second cause. For example, a display for switching display of a liquid crystal panel for the duration of one display field to repeat a data screen and a black screen alternately is known (refer to JP-A-2001-42282 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). A liquid crystal display for detecting motion of an input image signal and continuing to light a backlight if the motion is less than a predetermined value or intermittently lighting the backlight if the motion is equal to or greater than the predetermined value (refer to JP-A-2002-091400) and a display for producing pseudo impulse display made close to impulse display by blinking a backlight (refer to JP-A-2001-268603) are devised. Particularly, if the black insertion time period during the duration of one display field is prolonged, display is made closer to impulse display, so that sensuous moving image display performance improves.